U.S. Pat. No. 4,936,661, issued Jun. 26, 1990, to E. I. Betensky et al., describes a zoom lens with a short back focal length and having, from front to rear, negative, positive and negative optical units. The negative unit closest to the image is movable during zooming to provide a majority of the change in focal length. In some of the examples, the front two units move as a single optical group during zooming, and in others they move relative to each other during zooming.
Other similar zoom lenses are shown in U.S. Pat. Nos. 4,836,660 and 4,720,179, issued Jun. 6, 1989 and Jan. 19, 1988, respectively, to Ito; U.S. Pat. No. 4,854,683, issued Aug. 8, 1989, to Ozawa; U.S. Pat. Nos. 4,953,957, issued Sep, 4, 1990, to Kobayashi; 4,889,416, issued Dec. 26, 1989, to Yamada; 4,993,814, issued Feb. 19, 1991, to Hata; 4,787,718, issued Nov. 29, 1988, to Cho; 4,830,476, issued May 16, 1989, to Aoki; and 4,818,081, issued. Apr. 4, 1989, to Ito.